For weight saving in motor vehicle construction, components that have characteristics and relative thicknesses adapted to the loads occurring are used. This makes it necessary to weld components, in particular steel components, of different characteristics and/or different thicknesses to one another, for example a thin metal sheet to two thicker metal sheets. In addition, the increasing demand for lightweight designs to obtain further weight saving in the motor vehicle sector is giving preeminence to the use of sandwich sheets, which have for example thin metal sheets as outer layers and a layer of plastic arranged in between. These sandwich sheets may have characteristics such as a low weight with at the same time high strength. What is more, they can be sound-damping and offer great stiffness. Sandwich sheets too often have to be connected to further components by means of welding. In particular in vehicle bodyshell work, resistance welding, in particular resistance spot welding, is often used.
However, it is problematic for example that the aforementioned great differences in thickness or different characteristics of the components to be welded may also have the effect that, although the thicker components are welded to one another, thin metal sheets are not completely fused by the weld nugget or are not fused at all. This means that thin sheets cannot be connected to the further components in a reliable process. This is caused by process-dependent limitations, such as the distribution of the current density in dependence on the electrical resistance. In order to counteract this, it is known to achieve targeted control of the depth of the weld spot, by providing an additional input of heat. For example, an intermediate strip may be provided between a welding electrode and a thin metal sheet, so that as a result an increase in the interface resistance between the electrode and the thin sheet is achieved. Special electrodes, for example of tungsten, may also be used in order to achieve a further input of heat. A disadvantage of this, however, is that such solutions cannot be implemented cost-effectively in mass production on account of high costs or increased plant maintenance.